The Case CCC Radiation Resources Core Facility (RRCF) provides an essential service to the Cancer Center, since ionizing radiation has both carcinogenic and therapeutic roles in cancer and can produce viable, but non-reproductive cells for a variety of other studies. The Facility serves two types of cancer researchers: those studying the cancer-causing and cancer-treating actions of radiation, and those with primary interests in other topics for whom radiation is an essential tool, e.g., for killing cells to prepare feeder layers for growth of embryonic stem cells, or to study the immunogenic properties of cancer cells. The objectives of the RRCF are: 1) To maintain and operate ionizing radiation-producing devices for cancer researchers; 2) To consult with users concerning the instrumentation, the services, the training requirements, and if desired, the experimental design; 3) To train new users in proper operation of the equipment; and; 4) To provide support for implementation of new security regulations. The Radiation Resources Core supports researchers from 7 of the 8 Scientific Research Programs, with the heaviest use by the Hematopoietic Disorders Program. The RRCF supports research concerning the effects of radiation in which the interest is to determine the mechanism of its action or to improve radiation therapeutics. The facility also provides extensive services for those with other interests in cancer research, but for whom radiation is necessary for the construction of feeder layers, the ablation of the immune response of animals, or the sterilization of reagents, as exemplified by published studies of several other cancer researchers. For both categories of Cancer Center researchers, the RRCF is an essential resource without which their research could not be accomplished.